Power supply apparatuses become indispensable electronic devices for many kinds of electrical apparatuses. Nowadays, with increasing awareness of environmental protection, more and more electrical apparatuses are designed in views of power-saving concepts. Therefore, it is very important to increase the operating efficiency of the electrical apparatus. A power supply apparatus principally comprises switching elements, a magnetic element, capacitors and conductors of various resistance values. The magnetic element such as a transformer has become an essential electronic component for voltage regulation into required voltages for various kinds of electric appliances. For increasing the operating efficiency of the power supply apparatus, the loss of the magnetic element needs to be minimized. Generally, the loss of the magnetic element includes core loss, coil loss and terminal loss. The term “terminal loss” denotes the power loss generated at the soldered junction between the outlet terminal of a coil and a conductor.
FIG. 1 is a schematic perspective view illustrating a transformer and a rectifier that are mounted on a system circuit board according to the prior art. The transformer 10 and the rectifier 14 are mounted on the system circuit board 1. The rectifier 14 is located at an edge of the system circuit board 1. The outlet terminals 111 of the secondary winding coil 11 of the transformer 10 are welded on corresponding pins 12 of the system circuit board by a solder material 13. In addition, the transformer 10 is electrically connected to the rectifier 14 through a trace pattern (not shown) on the system circuit board 1. The transformer can output a sensing voltage to the rectifier 14. After the sensing voltage is rectified and filtered by the rectifier 14, a regulated DC voltage will be transmitted to a load (not shown).
Although the assembly structure of FIG. 1 is effective to provide a regulated DC voltage to the load, there are still some drawbacks. For example, since the outlet terminals 111 of the secondary winding coil 11 of the transformer 10 are welded on the pins 12 by the solder material 13, the relatively higher resistance of the solder material 13 may increase power loss of the transformer 10. In addition, since the transformer 10 is electrically connected to the rectifier 14 through the trace pattern on the system circuit board 1, the output current of the transform 10 is transmitted to the rectifier 14 through the pins 12 and the trace pattern. Since the rectifier 14 is usually located at an edge of the system circuit board 1, this very long path of the trance pattern results in additional power loss and increased leakage inductance.
Therefore, there is a need of providing an improved assembly structure of a transformer, a system circuit board and an auxiliary circuit board so as to obviate the drawbacks encountered from the prior art.